Removal of oxids from ferrous metal



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Patented Feb. 28, 1933 Cross Reference PATENT OFFICE FRANKLIN STOCKTON, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TO AMERICAN SHEET AND TIN PLATE COMPANY,

A CORPORATION OF NEW JERSEY REMOVAL OF OXIDS FROM FERROUS METAL ll'o Drawing.

This invention relates to the treating of ferrous metal to remove the oxid or scale and while not limited thereto, relates more particularly to a method of treating ferrous metal articles having an oxid or scale thereon which is particularly resistant to acid and, therefore, is not readily removable by the ordinary or well-known acid pickling without the use of excessively strong acid solul0 tions and long time immersions which result in badly etched 'or acid eaten surfaces on the articles.

The present invention is an improvement on the method described and claimed in United States Patent No. 1,572,848, issued to Rudyard Porter and Joshua C. Whetzel on February 9th, 1926, and has for its object the provision of an improved method whereby the acid resisting oxid or scale of the most resistant nature, such as that found on some classes of stainless steel, will have its acid resisting qualities broken down prior to acid pickling, thus eliminating the use of exceedingly strong acid pickling solutions and maiterially reducing the time of immersion in the acid bath. The present method permits a considerable saving in acid and produces a superior quality of oxid-free and scale-free articles, the faces of which are not etched by the acid.

This invention is particularly adaptable to removing the oxid or scale formed on stainless steel (in which term I include numerous steel alloys known by this or other names which are highly resistant to corrosion), especially the oxid resulting from annealing stainless steel since such oxid is especially resistant to acidremoval.

In carrying out this invention the metal containin the oxid is first immersed in a strong al aline and oxidizingsolution, a so- 29. 1. 9f ustic,,.a1ka1i u h, a 805M176 V, Hydroxid (NaOH) and an oxidizing agent sucu'aspotassium perman ana'te (KMnO,)

is prefarable. The strengt of the solution may vary but it has been found that a solution having approximatehLZO ner cent. smliuah m and eflmesia atelltrs nts w en heate to a temperature of approxi- Application flied January 18, 1930. Serial No. 421,816.

mately 190 degrees Fahrenheit. The action of this solution is to break down the resistance of the oxid or scale to acid so that it is readily removable by acid pickling.

In practicing the method of the Porter and Whetzel patent noted above, it was found that it was extremely difiicult to break down .the acid resistant quality of the more adherent types of scale on stainless steel, while the present method will efficiently no break down the acid resistant quality of the most resistant oxids.

In the treatment of stainless steel it has been found that immersion of the oxid or scale coated article in the above solution for 5 approximately 10 to 15 minutes is suflicient to break down the resistance of the oxid to the acid. The same results may be accomplished, however, with a weaker or cooler solution with longer time of immersion. In other words, the time of immersion varies inversely to the strength and temperature of the solution.

It will, of course, be understood that with F g-miss! oxids less resistant than those found on stainless steel, the period of immersion in the above solution is materially shorter.

Afterthearticle.,hasrheenrtreated.by sufli-' L t..immcrsicn.inrtheeatme.described alkaline solution it isthenuimmersed in an acid pickling ba th to completely remove the oxid g scale, and, due to the fact that the resistance of the oxid to the acid has been broken down by the prior alkaline and oxidizing solution, a comparativel short immersion in a weak acid solution 15 all that is necessa to remove the oxid.

he acid pickling bath is preferably composed of aqueous hydrochloric acid containing an inhibitor and this bath is maintained an at approximately 180 degrees Fahrenheit. The. metal is preferably maintained in the above acid bath from five to ten minutes.

It will be understood that this method is not limited to the use of 'a hydrochloric acid bath any ar strong acid, such as sulfuria nitric ma be used instead of the hydrochloric ac' The use of ahydrochloric acid pickle bath is preferable due to the fact that it results in the metal surface having a slightly superior color or luster. Thepreferred minimum concentration of the hydrochloric acid bath is approximately 2 per cent. while the preferred minimum temperature is approximately 120 degrees Fahrenheit.

It will be understood that this invention is not limited to the use of an alkaline and oxidizing solution having the preferred ingredients and proportions set 'forth above since other alkaline materials and varying proportions of the sodium hydroxid may be used. Also, various goncentrations of p as iuiape ma'naaaataareefiientiremgi from 0.1 er cent..to.pr solution in the alkali. It will also be noted that good results may be obtained by substituting other oxidizing agents such as manganese dioxide for the potassium permanganate.

Heretofore in the acid pickling of stainless steel to remove the oxid or scale, relatively strong acid solutions have been necessary with long immersions, which resulted in badly etched surfaces, while with the present method the surfaces of the pickled articles are substantially free from etching.

In carrying out this method the surfaces of the sheets have been cleaned with various strengths of acids, by varying the tempera,- ture and time of immersion, using higher strength acid at the lower temperatures and lower strength acid at the higher temperatures.

It will be understood that the percentages and temperatures given herein are only given for purposes of illustration and not as limitations, and also while the method has been particularly described in connection with the treatment of stainless steel, it is not limited to the treatment of such steel. but may be used in the treatment of any or all ferrous metals.

I claim:

1. The method of removing oxid in the form of scale resulting from heating ferrous metal articles from said articles which includes as a step the immersion of the articles in a solution containing approximately 20 per cent. sodium hydroxid (NaOH) and approximately 1 per cent. potassium permanganate (KMnO,).

2. The method of removing oxid from ferrous metal articles consisting in first immersing the articles in a hot bath consisting of approximately 20 per cent. sodium hydroxide (NaOH) and approximately 1 per cent. of potassium permanganate (KMnO,) to break down the resistance of the oxid, and then immersing the articles so treated in a hot acid pickling bath consisting of a solution of one of the usual pickling acids such as hydrochloric. nitric or sulfuric.

h Inlwitness whereof, I have hereunto set my FRANKLIN STOCKTON.

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